Dynamic control systems for automotive vehicles have recently begun to be offered on various products. Dynamic control systems typically control the yaw of the vehicle by controlling the braking effort at the various wheels of the vehicle. Yaw control systems typically compare the desired direction of the vehicle based upon the steering wheel angle and the direction of travel. By regulating the amount of braking at each corner of the vehicle, the desired direction of travel may be maintained. Typically, the dynamic control systems do not address roll of the vehicle. For high profile vehicles in particular, it would be desirable to control the rollover characteristic of the vehicle to maintain the vehicle position with respect to the road. That is, it is desirable to maintain contact of each of the four tires of the vehicle on the road.
In vehicle rollover control, it is desired to alter the vehicle attitude such that its motion along the roll direction is prevented from achieving a predetermined limit (rollover limit) with the aid of the actuation from the available active systems such as controllable brake system, steering system and suspension system. Although the vehicle attitude is well defined, direct measurement is usually impossible.
There are two types of vehicle attitudes needed to be distinguished. One is the so-called global attitude, which is sensed by the angular rate sensors. The other is the relative attitude, which measures the relative angular positions of the vehicle with respect to the road surface on which the vehicle is driven. The global attitude of the vehicle is relative to an earth frame (or called the inertia frame), sea level, or a flat road. It can be directly related to the three angular rate gyro sensors. While the relative attitude of the vehicle measures the relative angular positions of the vehicle with respect to the road surface, which are always of various terrains. Unlike the global attitude, there are no gyro-type sensors which can be directly related to the relative attitude. A reasonable estimate is that a successful relative attitude sensing system must utilize both the gyro-type sensors (when the road becomes flat, the relative attitude sensing system recovers the global attitude) and some other sensor signals.
One reason to distinguish relative and global attitude is due to the fact that vehicles are usually driven on a 3-dimensional road surface of different terrains, not always on a flat road surface. Driving on a road surface with large road bank does increase the rollover tendency, i.e., a large output from the global attitude sensing system might well imply an uncontrollable rollover event regardless of the flat road driving and the 3-D road driving. However driving on a three-dimensional road with moderate road bank angle, the global attitude may not be able to provide enough fidelity for a rollover event to be distinguished. Vehicular rollover happens when one side of the vehicle is lifted from the road surface with a long duration of time without returning back. If a vehicle is driven on a banked road, the global attitude sensing system will pick up certain attitude information even when the vehicle does not experience any wheel lifting (four wheels are always contacting the road surface). Hence a measure of the relative angular positions of the vehicle with respect to the portion of the road surface on which the vehicle is driven provides more fidelity than global attitude to sense the rollover event.
The vehicle rollover sensing system used for deploying safety-related devices has been proposed in U.S. Pat. Nos. 6,002,975, 6,038,495, EP 1002709A2, where a stand-alone sensor module including 5 sensors are used including the roll/pitch angular rate sensors, later/longitudinal/vertical acceleration sensors. These systems sense the global attitude of a vehicle without considering the relative attitude of the vehicle with respect to the road surfaces. Due to the stand-alone nature of the sensing module, it does not share internal information with vehicle dynamics control systems.
The rollover control system using brake controls has been proposed in U.S. Pat. No. 6,065,558 (“Anti-Rollover Brake System”), where the claimed sensor setting could be any of the following: (1) a lateral accelerometer; (2) a sensor for measuring the body roll angle; (3) an accelerometer, a gyroscope, a roll rate senor, and sensors measuring the distances between the vehicle and the wheels to measure the roll angle of the vehicle. In the current invention, a different sensor set is used. The used sensors includes those used in the vehicle yaw stability control (lateral/longitudinal accelerometers, yaw angular rate sensor, wheel speeds and steering angle) and an extra roll rate angular sensor. Also, notice that U.S. Pat. No. 6,065,558 does not intend to distinguish between global and relative attitude of a vehicle reflected by the Euler angles.
Another vehicle attitude sensing method has been proposed in U.S. Pat. No. 5,408,411 (“System For Predicting Behavior Of Automotive Vehicle And For Controlling Vehicular Behavior Based Thereon”). Where a sensor module using six linear accelerations is mounted on the vehicle to get vehicular attitude information.
It would therefore be desirable to provide an attitude control system to predict attitude angle for vehicle dynamics control that includes the interdependency among the roll, pitch and yaw motions while compensating for long term maneuvers.